AsianScientist (Aug. 19, 2011) - Shengping Gong, Junfeng Li, and Xiangyuan Zeng of Tsinghua University in Beijing, China, have published an article in Research in Astronomy and Astrophysics (RAA), proposing to place a small spacecraft with a solar sail into a retrograde orbit to prevent an asteroid from colliding with the Earth in 2036.

Near Earth Asteroids have a possibility of impacting with the Earth and always have a thread on the Earth.

The asteroid Apophis - which is 270 meters in diameter - will approach Earth at a distance of 37,000 to 38,000 km in 2029. In 2036, Apophis may come back and collide with Earth on April 13, 2036.

Using a solar sail in a H-reversal trajectory (retrograde orbit), the team proposes a way of changing the trajectory of the asteroid to avoid the impaction.

The impact velocity depends on two important parameters: the minimum solar distance along the trajectory and lightness number. A larger lightness number and a smaller solar distance lead to a higher impact velocity.

The results show that a 10 kg solar sail with a lead-time of one year will give the spacecraft an impact velocity of 90 km per second which - if done well enough in advance - can move Apophis out of a 600-m keyhole area in 2029 to prevent its return to Earth in 2036.

However, the spacecraft could go wildly off course, with variations in solar wind patterns, according to Technologyreview.com.

The asteroid, discovered in 2004, is considered the largest threat to our planet, although NASA scientists say the 2036 strike is unlikely, and the asteroid would likely disintegrate into smaller parts and make smaller collisions with Earth.